This invention relates to compositions and methods for cleaning and removing oleaginous materials from reinforced fiber composites. The proximity of aircraft landing gear doors and horizontal stabilizers to hydraulic fluid (HF) reservoirs leaves composite parts vulnerable to fluid contamination. As aircraft age, this problem is exacerbated, as damaged reservoirs and lines leak operational fluids into open regions, particularly core cells of composite honeycomb. While the majority of these oleaginous fluids are not inherently damaging to the structural materials, residual fluids interfere with bonded patch repair. Without a consistent method to effectively remove hydraulic fluid contamination to enable reliable bonded repairs, repairing the contaminated parts will not be achievable.
The traditional method to remove hydraulic fluid contamination prior to the application of the bonded composite repair patch involves packing the contaminated area with breather cloth and heating at an elevated temperature under vacuum. The current procedure for removing hydraulic fluids from composite materials is costly and time consuming. Methyl-isobutyl ketone (MIBK) is used to remove hydraulic fluid from most composite materials. MIBK is ineffective in the removal of hydraulic fluid from composite materials; however, it has been used because it does not pose a threat to the workers. Due to the limited number of controlled environments to perform this process while aircraft are deployed, it is necessary to use solvents that are environmentally friendly and present minimum risk to workers.
More specifically, aircraft composite structures often become contaminated by various aircraft maintenance fluids during the course of normal operation. For example, hydraulic fluid contamination can cause composite plasticization, delamination and disbanding from honeycomb core. Additionally, hydraulic fluid contamination must be addressed prior to a bonded repair. The solvent of choice for cleaning composite structures has historically been hexane, which efficiently removes hydraulic fluid contamination without adversely affecting composite properties. However, hexane is a hazardous chemical with a low flash point and must be used in a controlled environment to prevent worker exposure. Therefore, any new cleaner must be environmentally-advantaged, less hazardous, and most importantly, must be effective in removing the hydraulic fluid from the composite materials without affecting their mechanical and thermal properties.
Accordingly, it is an object of this invention to provide a non-aqueous fluid composition for cleaning and removing oleaginous materials such as hydraulic fluids from reinforced fiber composites.
It is another object of this invention to provide a method of cleaning and removing oleaginous materials from reinforced graphite fiber composites with a non-aqueous fluid composition characterized as being free of ozone depletion materials, having a low vapor pressure, and a flash point above 140° F.